This application is designed to address the molecular basis of malaria-associated anemia, one of the most prevalent and often life-threatening manifestations of infection with the malaria parasite. Hundreds of millions of people have clinical malaria infections every year and thus the impact of the disease on human health is profound. During the process by which the parasites invade erythrocytesto allow them to multiply within, parasite molecules bind to the surface of these cells. It is proposed that these molecules, which are also shed from the parasite, bind to uninfected erythrocytes in the infected host and promote the destruction and clearance of uninfected red blood cells, thus contributing to anemia. Furthermore it is proposed to test the hypothesis that specific antibodies to such molecules promote this clearance. Two molecular complexes consisting of abundant proteins that have been implicated in binding to host erythrocytes will be examined to define their structure, diversity and function. The components responsible for binding to red cells and their role in red blood cell invasion will be clarified. Their specific interactions with molecules of the erythrocyte membrane will be defined, and their pontential to exacerbate anemia examined in field-based studies. The properties of parasite lines in which specific genes, coding for components of one of these molecular complexes, have been deleted will be studied. The phenotype of these modified parasites may be expressed as a change of host cell specificity, or different growth rate, or in an alteration of the parasite- host balance. It is proposed that these genetically manipulated parasites can disturb the mechanisms that maintain the red cell equilibrium, leading to dysfunctional control of red cell numbers and consequent anemia. It will be important to establish whether molecules that are potential malaria vaccine candidates are also the targets of immune mechanisms that promote anemia.